Life on Earth

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This tree diagram shows the relationships between several groups of organisms.

The root of the current tree connects the organisms featured in this tree to their containing group and the rest of the Tree of Life. The basal branching point in the tree represents the ancestor of the other groups in the tree. This ancestor diversified over time into several descendent subgroups, which are represented as internal nodes and terminal taxa to the right.

You can click on the root to travel down the Tree of Life all the way to the root of all Life, and you can click on the names of descendent subgroups to travel up the Tree of Life all the way to individual species.

The rooting of the Tree of Life, and the relationships of the major lineages, are controversial. The monophyly of Archaea is uncertain, and recent evidence for ancient lateral transfers of genes indicates that a highly complex model is needed to adequately represent the phylogenetic relationships among the major lineages of Life. We hope to provide a comprehensive discussion of these issues on this page soon. For the time being, please refer to the papers listed in the References section.

Discussion of Phylogenetic Relationships

Two alternative views on the relationship of the major lineages (omitting viruses) are shown below

The "archaea tree":

The "eocyte tree":

References

Baldauf, S. L., J. D. Palmer, and W. F. Doolittle. 1996. The root of the universal tree and the origin of eukaryotes based on elongation factor phylogeny. Proceedings of the National Academy of Sciences of the United States of America 93:7749-7754.

Becerra, A., L. Delaye, S. Islas, and A. Lazcano. 2007. The very early stages of biological evolution and the nature of the last common ancestor of the three major cell domains. Annual Review of Ecology, Evolution, and Systematics 38:361-379.

Benachenhou, L. N., P. Forterre and B. Labedan. 1993. Evolution of glutamate dehydrogenase genes: Evidence for two paralogous protein families and unusual branching patterns of the archaebacteria in the universal tree of life. Journal Of Molecular Evolution 36:335-346.

Brown, J. R. and W. F. Doolittle. 1995. Root of the universal tree of life based on ancient aminoacyl-tRNA synthetase gene duplications. Proceedings of the National Academy of Sciences of the United States of America 92:2441-2445.

Cavalier-Smith, T. 2002. The neomuran origin of archaebacteria, the negibacterial root of the universal tree and bacterial megaclassification. International Journal of Systematic and Evolutionay Microbiology 52:7-76.

Feng, D.-F., G. Cho, and R.F. Doolittle. 1997. Determining divergence times with a protein clock: Update and reevaluation. Proceedings of the National Academy of Sciences of the United States of America 94:13028-13033.

Gribaldo, S. and P. Cammarano. 1998. The root of the universal tree of life inferred from anciently duplicated genes encoding components of the protein-targeting machinery. Journal of Molecular Evolution 47:508-516.

Gupta, R. S. 1998. What are archaebacteria: Life's third domain or monoderm prokaryotes related to Gram-positive bacteria? A new proposal for the classification of prokaryotic organisms. Molecular Microbiology 29:695-707.

Lake, J.A., E. Henderson, M. Oakes, M.W. Clark. 1984. Eocytes: a new ribosome structure indicates a kingdom with close relationship to eukaryotes. Proceedings of the National Academy of Sciences (USA) 81:3786-3790.

Lawson, F. S., R. L. Charlebois, and J.-A. R. Dillon. 1996. Phylogenetic analysis of carbamoylphosphate synthetase genes: complex evolutionary history includes an internal duplication within a gene which can root the Tree of Life. Molecular Biology and Evolution 13:970-977.

Moreira, D. and P. Lopez-Garcia. 1998. Symbiosis between methanogenic archaea and delta-proteobacteria as the origin of eukaryotes: the syntrophic hypothesis. Journal of Molecular Evolution 47:517-530.

Nealson, K. H. and P. G. Conrad. 1999. Life: past, present and future. Philosophical Transactions of the Royal Society of London Series B 354:1923-1939.

Skophammer, R. G., C. W. Herbold, M. C. Rivera, J. A. Servin, and J. A. Lake. 2006. Evidence that the Root of the Tree of Life Is Not within the Archaea. Molecular Biology and Evolution 23(9):1648-1651.

Woese, C. 1998. The universal ancestor. Proceedings of the National Academy of Sciences (USA) 95:6854-6859.

Woese, C. R., O. Kandler, and M. L. Wheelis. 1990. Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya. Proceedings of the National Academy of Sciences (USA) 87:4576-4579.

Cell of the Archaean Sulfolobus infected by virus STSV1 observed under microscopy. Two spindle-shaped viruses were being released from the host cell. The strain of Sulfolobus and STSV1 were isolated by Xiaoyu Xiang and his colleagues in an acidic hot spring in Yunnan Province, China. At present, STSV1 is the largest archaeal virus that has been isolated and studied. Its genome sequence has been sequenced.

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Page: Tree of Life
Life on Earth.
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Citing this page:

Tree of Life Web Project.
1997. Life on Earth.
Version 01 January 1997 (temporary). http://tolweb.org/Life_on_Earth/1/1997.01.01in The Tree of Life Web Project, http://tolweb.org/

Each ToL branch page provides a synopsis of the characteristics of
a group of organisms representing a branch of the Tree of Life. The
major distinction between a branch and a leaf of
the Tree of Life is that each branch can be further subdivided into
descendent branches, that is, subgroups representing distinct genetic
lineages.